function identify() {
  return this.name.toUpperCase()
}

function speak() {
  var greeting = "hello, I am" + identify.call(this)
  console.log(greeting)
}

var me = {
  name: 'wn'
}
var you = {
  name: 'zj'
}
// let result = identify.call(me)
// console.log(result)
speak.call(me)